Inhibition of calcium-dependent pathways of B-cell activation by DMBA.

The purpose of the experiments described in these studies was to determine the effects of 7,12-dimethylbenz[a]anthracene (DMBA) on B-cell activation produced by anti-IgD antibodies and interleukin-4 (IL-4). B and T cells are known to share many of the same biochemical pathways for cell activation by mitogen and antigen receptors. Previous studies in this laboratory have shown that DMBA inhibits mitogen-induced Ca2+ mobilization in murine and human T cells and produces an increase in intracellular Ca2+ in resting cells. The results of the present studies demonstrate that DMBA increases Ca2+ in resting B cells and inhibits B cell activation produced by anti-IgD antibodies, as measured by mobilization of free intracellular Ca2+ and [3H]thymidine incorporation. The proliferative response of B cells to insolubilized anti-IgD was suppressed only when cells were preexposed to DMBA. In contrast, IL-4 pathways of B-cell activation were insensitive to inhibition by DMBA, even when cells were preexposed. The induction of Class II MHC antigen (Ia) antigens on B cells by IL-4 was also found to be insensitive to DMBA treatment. These results suggest that DMBA suppresses only Ca(2+)-dependent pathways of B cell activation and indicate that altered Ca2+ homeostasis may be responsible for immunosuppression induced by this agent.